Method of forming NiP nonmagnetic film and method of manufacturing magnetic head using the film

ABSTRACT

The method is capable of easily and securely forming a NiP nonmagnetic film. In the method of forming the NiP nonmagnetic film by electrolytic plating, the electrolytic plating is performed in NiP plating solution consisting of: a reagent for supplying nickel ions; a reagent for supplying phosphorus ions; and a reagent including carboxyl groups. For example, sulfates and chloride salts of nickel, etc. may be use as the reagent for supplying nickel ions; phosphorus acid, sodium phosphite, etc. may be used as the reagent for supplying phosphorus ions.

BACKGROUND OF THE INVENTION

The present invention relates to a method of forming a NiP nonmagnetic film and a method of manufacturing a magnetic head using the NiP nonmagnetic film, more precisely relates to a method of forming a NiP nonmagnetic film by electrolytic plating and a method of manufacturing a magnetic head using said NiP nonmagnetic film.

FIG. 6 is a sectional view showing a layered structure of a read-head and a write-head of a magnetic head, and FIG. 7 is an explanation view of the read-head and the write-head seen from an air bearing surface of the magnetic head. The magnetic head 10 has a read-head 20 and a write-head 30, which are layered on a substrate. The read-head 20 is constituted by forming an MR element 23 between a lower shielding layer 21 and an upper shielding layer 24. In the write-head 30, a write-gap layer 33 is formed between the upper shielding layer 22, which is commonly used as a lower magnetic pole 31 of the write-head 30, and an upper magnetic pole 32; conductive coils 34 are formed in a back gap section, which is formed between the lower magnetic pole 31 and the upper magnetic pole 32.

The lower magnetic pole 31 and the upper magnetic pole 32 are made of a metal having high saturation magnetic flux density; the write-gap layer 33 is made of a nonmagnetic material. As shown in the drawings, tip pole parts 31 a and 32 a are respectively formed at front ends of the magnetic poles 31 and 32 of the magnetic head 10, so that core width of the write-head 30 is narrow.

The lower magnetic pole 31 and the upper magnetic pole 32 are formed by a plating method, which is a superior method with high deposition efficiency. However, in the plating method, a plating metal is deposited in grooves of resist patterns so as to form magnetic poles. Therefore, the core width cannot be sufficiently narrow due to aspect ratio of the patterns. The core width influences accuracy of track width, so the core width is an important factor to increase recording density of recording media. Thus, the core width has been made narrow by ion trimming after the plating. However, if the core width is made narrow by ion trimming, materials forming the magnetic poles and the write-gap layer stick onto the core again, so that accuracy of the track width must be lowered.

To solve the problem of the lowering of the accuracy of the track width, the write-gap layer is made of a nonmagnetic material, e.g., NiP; and the lower magnetic pole, the write-gap layer and the upper magnetic pole are layered in this order by plating (see Japanese Patent Gazette No. 2002-157704). Nip of the write-gap layer is made by including a prescribed amount of phosphorus (P) in nickel (Ni), which is a magnetic material, so that NiP becomes a nonmagnetic material. Therefore, the amount of P is important. If the NiP layer is formed on a magnetic plated layer, e.g., the lower magnetic pole, the amount of P of the NiP layer is reduced in a part close to a boundary surface between the layers, so that the NiP layer has magnetism in the part. To solve this problem, the NiP layer is formed by supplying a pulsed current (see Japanese Patent Gazette No. 2002-175607), or a seed layer for plating a NiP layer is formed on a lower magnetic pole (see Japanese Patent Gazette No. 2002-298310).

However, in the method of forming the write-gap layer made of NiP layer by plating, it is difficult to sufficiently prevent the reduction of P at the beginning of the plating. If the amount of P constituting the NiP layer is reduced, the NiP layer has magnetism so that substantial thickness of the write-gap layer must be thinner than desired thickness. Therefore, recording characteristics of the magnetic head must be worse. The thickness of the NiP layer of the write-gap layer having magnetism is varied according to plating conditions, so the substantial thickness is different with respect to each lot or each element. Therefore, reliability of conventional magnetic head must be lowered.

Note that, besides the write-gap layer, the magnetic head further has a separation layer, which separates the lower magnetic pole from the shielding layer, and a protection layer, which covers a surface of the upper magnetic pole. These nonmagnetic layers may be made of an insulating material. If they are made of a nonmagnetic metallic material, e.g., NiP, they can be formed by plating. Further, the magnetic head, which has the layered structure, can be completely formed a series of plating steps, so that efficiency of the process of manufacturing the magnetic head can be improved.

SUMMARY OF THE INVENTION

An object of the present invention is to provide a method of easily and securely forming a NiP nonmagnetic film.

Another object is to provide a method of manufacturing a magnetic head using the NiP nonmagnetic film of the present invention.

To achieve the objects, the present invention has following characteristics.

Namely, in the method of forming a NiP nonmagnetic film by electrolytic plating, the electrolytic plating is performed in NiP plating solution consisting of: a reagent for supplying nickel ions; a reagent for supplying phosphorus ions; and a reagent including carboxyl groups. For example, sulfates and chloride salts of nickel, etc. may be use as the reagent for supplying nickel ions; phosphorus acid, sodium phosphite, etc. may be used as the reagent for supplying phosphorus ions.

In the method, both of an organic reagent and an inorganic reagent can be used as the reagent including carboxyl groups. For example, sodium citrate may be used as the reagent.

In the method, rate of depositing the NiP film may be 0.01-0.04 μm/min. In this case, a sufficient amount of P, which removes magnetism from the NiP film, can be included in the NiP film from the beginning of the electrolytic plating. Therefore, sufficient amount of P can be uniformly and stably distributed in the entire film.

In the method, current density of a plating current may be 5 mA/cm² or more. In this case, deposition rate of the NiP film can be maintained, and the plating can be performed without dissolving a base metal layer.

Considering corrosion resistance of the base layer of the NiP film and resistance of resist for patterning the NiP film, a preferable pH value of the NiP plating solution is 4-8.

Further, in the method of manufacturing a magnetic head including: a plurality of magnetic films, which are formed as magnetic poles or magnetic shielding layers; and a NiP nonmagnetic film, which are formed as a separation layer separating the magnetic films or a protection layer covering a surface of the magnetic film, the NiP nonmagnetic film is formed by the above described method of the present invention. By employing the method of forming the NiP nonmagnetic film, the nonmagnetic film of the magnetic head can be easily and securely formed by the electrolytic plating, so that a manufacturing process of the magnetic head can be simplified. The NiP film can become the entirely nonmagnetic film, variation of substantial thickness of the nonmagnetic films can be prevented, so that reliability of the magnetic heads can be improved.

The NiP nonmagnetic film is used in a write-gap layer, which is formed between a lower magnetic pole and an upper magnetic pole, so that a gap length can be fixed, so that variation of characteristics of magnetic heads can be prevented.

In the present invention, the NiP nonmagnetic film can be easily formed by the electrolytic plating. By employing the NiP nonmagnetic film of the present invention in the magnetic head, the magnetic head can be easily manufactured. Further, the NiP film can be entirely nonmagnetic in the direction of thickness, so the NiP film can be used in a write-gap layer, whose gap length must be precisely set. Therefore, the magnetic head having high accuracy and high reliability can be provided.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments of the present invention will now be described by way of examples and with reference to the accompanying drawings, in which:

FIG. 1 is a graph of amount of phosphorus (P) included in a NiP plated film with respect to thickness thereof;

FIG. 2 is a graph of amount of phosphorus (P) included in the NiP plated film with respect to deposition rate thereof;

FIG. 3 is a graph of the deposition rate of the NiP plated film with respect to concentration ratio between nickel ions and carboxyl groups, and plating currents;

FIG. 4 is a graph of amount of dissolving a FeCo plated film with respect to pH values of NiP plating solution;

FIG. 5 is a graph of variation of magnetism of the NiP film before and after annealing;

FIG. 6 is a sectional view showing a layered structure of the read-head and the write-head of the conventional magnetic head; and

FIG. 7 is an explanation view of the read-head and the write-head seen from the air bearing surface of the conventional magnetic head.

DETAILED DESCRIPTION OF THE EMBODIMENTS

Preferred embodiments of the present invention will now be described in detail with reference to the accompanying drawings.

An example of composition of NiP plating solution, which is used for forming a NiP nonmagnetic film by electrolytic plating, is shown in TABLE. The NiP plating solution includes: nickel sulfate and nickel chloride as reagents for supplying nickel (Ni); and phosphorus acid and sodium hydrogen phosphite as reagents for supplying phosphorus (P). Further, sodium citrate is added to the NiP plating solution as carboxylic acid.

Note that, the carboxylic acid to be added is not limited to sodium citrate. Other reagents including carboxyl groups may be used, but sodium tartrate, which easily forms deposits insoluble with Ni, cannot be used. TABLE Reagent Concentration Ratio (Mol/l) Nickel sulfate 0.095-0.19 Nickel chloride  0.03-0.06 Phosphorus acid 0.125-0.25 Sodium hydrogen phosphite 0.125-0.25 Sodium citrate 0.125-0.25

In the NiP plating solution, sulfate and chloride salt are used as a source for supplying nickel ions, but either of the two may be used. Phosphorus acid and sodium hydrogen phosphite are mixed as a source for supplying phosphorous ions. They need not be mixed, but a pH value of the plating solution can be easily adjusted by mixing strong acid (phosphorus acid) and a neutral compound (sodium hydrogen phosphite). Note that, the pH value of the NiP plating solution is finally adjusted by adding sulfuric acid or sodium hydroxide.

Amounts of phosphorus (P) with respect to thickness of NiP plated films, which were respectively formed in the conventional NiP solution and the NiP solution of the above described example, are shown in FIG. 1. The NiP films were formed on FeCo base layers by NiP plating. In the plating solution including sodium citrate, the amount of P was entirely maintained around 20 (at %) from the beginning.

Variation of magnetism of the NiP films with respect to the amount of P is shown in FIG. 5. Magnetic characteristics of the film immediately after the plating and the film annealed after the plating were different. By annealing the film for one hour at temperature of 250° C. magnetism was increased. According to FIG. 5, the amount of P in the NiP film was about 15 (at %) or more, even the annealed NiP film was a nonmagnetic film.

According to FIG. 1, in the NiP film formed in the conventional plating solution, the amount of P in the beginning of the film was small, and the thickness of the film having nonmagnetic composition (P ≧15 (at %)) was several dozen nm. On the other hand, in the NiP film formed in the solution including sodium citrate, the sufficient amount of P for nonmagnetism was included from the beginning of the film. Therefore, P was stably uniformly included in the entire film. Namely, the plating method of the present embodiment is capable of forming the NiP plated film, which is entirely nonmagnetic.

FIG. 2 shows a relationship between the amount of phosphorus (P) included in the NiP plated film with respect to deposition rate of the NiP film, which was formed by the electrolytic plating. According to the results, the amount of P was reduced with increasing the deposition rate of the NiP film. To maintain the amount of P in the NiP film 15 (at %) or more, the deposition rate of the NiP film should be about 0.04 (μm/min.) or less.

To form the NiP nonmagnetic film, which includes the proper amount of P, the deposition rate of the NiP film must be controlled, but the deposition rate is defined by concentration ratio between Ni ions and carboxyl groups in the plating solution and a plating current.

Variation of the deposition rate of the NiP plated film with respect to the concentration ratio between nickel ions and carboxyl groups and plating currents is shown in FIG. 3. To reduce the deposition rate of the NiP film about 0.04 (μm/min.) or less, the concentration ratio between Ni ions and carboxyl groups should be about 0.3 or less.

The deposition rate of the NiP film was reduced with reducing the plating current. In that case, an allowable range of the concentration ratio between Ni ions and carboxyl groups is broadened. However, if the plating current is too small, a plated film of a base layer will be dissolved when the NiP film is formed thereon. Preferably, the NiP film is plated with current density of the plating current about 5 mA/cm² or more, the deposition rate of about 0.01 (μm/min.) or more and the concentration ratio between Ni ions and carboxyl groups about 0.2 or more.

When the NiP nonmagnetic plated film is used as a write-gap layer of a magnetic head, thickness of the write-gap layer is about 100 nm, so the thickness is very thin. If the deposition rate is too high, distribution accuracy is lowered, so the deposition rate should be properly controlled so as to securely form the thin film.

However, if the NiP plated film is used as a cap layer for restraining reduction of a magnetic layer when trimming front ends of magnetic poles of the magnetic head, the thickness of the film should be formed on the micron scale. In that case, the film should be formed at relatively high deposition rate.

By selecting the plating current and the concentration ratio between Ni ions and carboxyl groups according to use of the NiP film, the deposition rate of forming the NiP plated film can be properly controlled.

Besides the above described conditions, a pH value too is an important condition of the NiP plating solution.

The lowest pH value of the NiP plating solution is defined by corrosion resistance of the base layer (plated layer) of the NiP film; the highest pH value of the NiP plating solution is defined by resistance properties of resist. Namely, the highest pH value of the NiP plating solution must not influence the resist, so the preferable highest pH value is 8 or less. For example, in case of forming the NiP film on a FeCo plated base layer, the preferable lowest pH value is about 4.

FIG. 4 shows a relationship between amount of dissolving edges of the FeCo plated film with respect to the pH values of the NiP plating solution.

According to FIG. 4, when the pH value of the NiP plating solution wais 4 or more, the amount of dissolving the edges of the FeCo plated film while forming the NiP film was 1/10 of total film thickness or less. When the NiP plated film is used in the write-gap layer of the magnetic head, if the amount of dissolving the base layer is 1/10 of the total film thickness or less, curvature can be restrained small so that the curvature can be removed by trimming the edges.

Example of Experiment

A NiP film was formed on a FeCo plated layer in the NiP plating solution, which was the above described example including sodium citrate and whose pH value was 4.5, with the concentration ratio between Ni ions and carboxyl groups Ni²+/COO⁻⁼0.22 and current density of 5 mA/cm^(2.)

In the NiP plated film, the concentration of P was about 22 (at %) and maintained in the entire film from the beginning of the film so that the NiP nonmagnetic film could be produced. Further, the deposition rate was fixed, so that the film having uniform desired thickness could be produced.

Note that, in case of forming a NiP film on a NiFe base film, which was formed by spattering NiFe, in the NiP plating solution, similar results were gained.

By the method of the present invention, the NiP nonmagnetic film, which is entirely nonmagnetic in the direction of thickness, can be easily and securely formed by the electrolytic plating. By employing the NiP nonmagnetic film of the present invention in the magnetic head, the reliable magnetic head can be easily and securely manufactured.

The magnetic head of the present embodiment has a layered structure of piling magnetic layers and nonmagnetic layers, e.g., a lower magnetic pole, a write-gap layer, an upper magnetic pole, as well as the conventional magnetic head shown in FIGS. 6 and 7. The nonmagnetic layers act as the write-gap layers, a separation layer the lower magnetic pole from the magnetic layer, and a protection layer covering a surface of the upper magnetic pole. These nonmagnetic layers are made of the NiP nonmagnetic film of the present invention.

In the method of the present invention, the nonmagnetic layers are made of NiP, which has electric conductivity. Unlike a method of forming nonmagnetic layers with electric insulation materials, the nonmagnetic layers can be formed in a series of plating steps, in which the lower magnetic pole and the upper magnetic pole are formed by electrolytic plating, so that the plating steps can be simplified and manufacturing efficiency can be improved.

And, the NiP film of the present invention can be entirely nonmagnetic, so substantial thickness (thickness of a nonmagnetic part) of the NiP film can be precisely controlled, variation of the substantial thickness during a manufacturing process can be restrained, and the magnetic head having high accuracy and high reliability can be manufactured.

Further, the nonmagnetic layers are made of the electric conductive material, damaging read-elements of the magnetic head, which is caused during the manufacturing process by static electricity, can be prevented.

The invention may be embodied in other specific forms without departing from the spirit of essential characteristics thereof. The present embodiments are therefore to be considered in all respects as illustrative and not restrictive, the scope of the invention being indicated by the appended claims rather than by the foregoing description and all changes which come within the meaning and range of equivalency of the claims are therefore intended to be embraced therein. 

1. A method of forming a NiP nonmagnetic film by electrolytic plating, wherein said electrolytic plating is performed in NiP plating solution including: a reagent for supplying nickel ions; a reagent for supplying phosphorus ions; and a reagent including carboxyl groups.
 2. The method according to claim 1, wherein the reagent including carboxyl groups is sodium citrate.
 3. The method according to claim 1, wherein rate of depositing said NiP film is 0.01-0.04 μm/min.
 4. The method according to claim 3, wherein current density of a plating current is 5 mA/cm² or more.
 5. The method according to claim 1, wherein a pH value of the NiP plating solution is 4-8.
 6. A method of manufacturing a magnetic head including: a plurality of magnetic films, which are formed as magnetic poles or magnetic shielding layers; and a NiP nonmagnetic film, which are formed as a separation layer separating the magnetic films or a protection layer covering a surface of the magnetic film by electrolytic plating, wherein said electrolytic plating is performed in NiP plating solution including: a reagent for supplying nickel ions; a reagent for supplying phosphorus ions; and a reagent including carboxyl groups.
 7. The method according to claim 6, wherein the reagent including carboxyl groups is sodium citrate.
 8. The method according to claim 6, wherein rate of depositing the NiP nonmagnetic film is 0.01-0.04 μm/Min.
 9. The method according to claim 8, wherein current density of a plating current is 5 mA/cm² or more.
 10. The method according to claim 6, wherein a pH value of the NiP plating solution is 4-8.
 11. The method according to claim 6, wherein the NiP nonmagnetic film is formed between a lower magnetic pole and an upper magnetic pole, which are made of magnetic films, as a write-gap layer. 